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Roadside sound barrier tracer study 2008
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Roadside sound barrier tracer study 2008
  • Corporate Authors:
    Air Resources Laboratory (U.S.)
  • Description:
    A roadway toxics dispersion study was conducted during the month of October at the NOAA Tracer Test Facility on the U.S. DOE's Idaho National Laboratory (INL) near Idaho Falls, ID. The Field Research Division (FRD) of NOAA, in conjunction with the Atmospheric Modeling and Analysis Division of the U.S. EPA, conducted the Roadside Sound Barrier Tracer Study (RSBTS08). The purpose of the study was to document the effects on concentrations of roadway emissions behind a roadside sound barrier in various conditions of atmospheric stability. Roadway emissions were simulated by the release of an atmospheric tracer (SF6) from two 54 m long line sources. A 90 m long, 6 m high mock sound barrier constructed of straw bales was installed on one grid while the other grid had no barrier. Simultaneous tracer concentration measurements were made with real-time and bag samplers on identical sampling grids downwind from the two line sources. An array of 6 sonic anemometers were employed to measure the barrier-induced turbulence. Supporting meteorological measurements came from infrastructure already in place at the test site including a radar wind profiler with RASS, a mini sodar, an eddy flux station, and nearby NOAA/INL Mesonet stations. The experiment was conducted in the pristine environment of the INL to enable clearer and less ambiguous interpretation of the data. Specifically, all confounding affects such as buildings, trees, roadway heating, and vehicle induced turbulence were eliminated allowing only the effect of the barrier to be studied in stable, unstable, and near neutral conditions. The results will augment those of a wind tunnel study conducted by the U.S. EPA in a similar manner to this field study. Key findings of the study are: (1) the areal extent of the concentration footprint downwind of the barrier was a function of atmospheric stability with the footprint expanding as stability increased; (2) normalized concentrations were a function of atmospheric stability, increasing in magnitude as atmospheric stability increased; (3) there was a concentration deficit in the wake zone of the barrier with respect to concentrations at the same grid locations on the non-barrier side at all atmospheric stabilities; (4) the concentration deficit region behind the barrier persisted downwind beyond the estimated flow reattachment point; (5) lateral dispersion was significantly greater on the barrier grid than the non-barrier grid; and (6) the barrier tended to trap high concentrations in the 'roadway' (i.e. upwind of the barrier) in low wind speed conditions, especially in stable conditions.

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